Significant research and development efforts are being made on an international scale to improve the efficiency and environmental performance for energy producing systems. Today about half of all such efforts are made within the renewable energy sector rather than for traditional fossil or nuclear fuel type thermal power production. It has become clear that energy storage will be a key technology for making further advances, and large investments are currently being made in developing such capabilities, notably by storing energy using rechargeable batteries, pumped hydro storage, compressed air, flywheels, conversion to hydrogen, and heat storage including heat storage with material phase change.
It is generally recognized that energy storage can facilitate time dependent adaptation of power delivery to consumers and the market in general, and it can provide security of delivery by way of bridging power delivery when the primary power production is insufficient or it fails.
For some types of renewable energy production having storage is absolutely necessary. One such field is concentrated solar power (CSP) where heat storage is used to compensate for insufficient or failing heat production, such as during day time when cloud cover occurs and during the night hours when there is no sun. In the case of CSP using parabolic trough collectors the heat is generated by reflected and focused sun rays heating oil in a pipe system; this oil is thereafter heat exchanged with molten salt which is stored in large, insulated storage tanks. The oil is a feasible mineral, organic or synthetic heat transfer oil, such as Therminol. When stored heat is needed for supplementary or extended energy production it is extracted by a reverse heat exchange between molten salt and oil. Thereafter the oil is once more heat exchanged into water-steam which in turn is used to produce electricity via turbines and electric generators. This technology has some severe disadvantages in that it involves using very expensive storage fluids such as molten salt, it requires multiple oil/salt heat exchangers, it needs at least two large molten salt storage tanks, it requires molten salt pumps and corresponding pumping energy to move the molten salt to and from the tanks, and there is a risk of the salt solidifying in pipes or other structures which can occur even at very high temperature.
Another version of CSP is where a large field of mirrors (heliostats) reflects sun rays onto a high tower where a receiver filled with a high temperature working fluid, such as molten salt, is used for photon-heat conversion. In the case of using molten salt as working fluid this fluid may be directly heat exchanged with water-steam to generate electric power using turbines and generators. Alternatively, the molten salt may be stored in large tanks for later to be used to generate electricity as explained above.
Recent research efforts also consider using steam as working fluid for the CSP tower technology; in this way heat exchangers from molten salt to steam may be avoided. The problem with direct steam technology is to be able to store the heat for delayed use, particularly combined with producing electricity effectively. The current invention provides a possible solution to this problem.
There are numerous traditional technologies where the main source of energy is heat and pressure; such as fossil fuel (coal, oil, gas) plants and nuclear power plants. Although such plants may not depend on having storage for periodical lack of energy production, heat storage may be a great advantage and economically profitable for such plants as well. For instance, heat storage may facilitate full use or better use of the heat production capability throughout a 24 hour day cycle since heat produced during the night may be fully or partly stored and provide higher energy production during the day time in accordance with market demands. Moreover, storage is of great value for providing continuity and security of energy supply or for dealing with temporal bottlenecks in the electric grid system.
The objective of the present invention is to provide a plant for production of energy, which plant is beneficial over the previous technology with respect to issues mentioned. Further, the plant storage should preferably:                Be able to simplify the overall process of heat accumulation, transportation and storage as compared with existing systems        Be able to operate with temperatures and pressures most suitable for the heat collection and transportation of heat to the storage        Be able to accommodate different types of working fluid deemed most suitable for the above mentioned operation        Be able to efficiently transport heat out of storage by way of fluids with temperature and pressure suitable for the heat extraction process        Be able to accommodate types of working fluids most suitable for the heat delivery from storage        Be able to operate in a primarily heat exchanger mode where the heat in the working fluid of the primary heat input pipe loop is heat exchanged directly and simultaneously within the storage heat exchangers with another type of working fluid in the heat extraction pipe system        Be suitable for implementation with already commercially available components such as pumps, valves, pipes, sensors, and control systems        Provide cost and efficiency advantages over existing systems        Be environmentally safe        Be easy to integrate within and modify existing facilities as well as for being used in design and operation of new facilities        